Hypertension is a strong risk factor for cardiovascular disease (CVD) and causes death and disability in our rapidly expanding older population. Although several health organizations recommend exercise for milder forms of hypertension, few older persons were subjects in the research upon which these recommendations are based. Because the hemodynamic causes of hypertension and the cardiovascular (CV) responses to exercise in older persons may differ from those of younger persons, the existing research on exercise and BP may not apply to older persons. Therefore, the specific aim of this study is to determine whether exercise training reduces BP in men and women, ages 55 to 75 years, with high normal BP or mild hypertension. Subjects will be randomized to 6- months of exercise training or to a control group. The type, intensity, duration, and frequency of exercise will follow the American College of Sports Medicine's guidelines for exercise and hypertension. Because so few older women were included in prior exercise studies, an equal number of older men and women will be enrolled to examine gender differences in the response to exercise training. We will also determine whether exercise mitigates detrimental changes in central and peripheral parameters of CV structure and function seen in hypertensive individuals. These parameters are left ventricular (LV) mass, LV filling rate, endothelial-mediated vasoreactivity, and vascular stiffness which will be assessed using a new generation of noninvasive techniques including high resolution ultrasound, doppler echocardiography, and high resolution magnetic resonance imaging (MRI). A finding that changes in BP are explained by any or some of these CV parameters would identify new potential pathophysiological mechanisms by which exercise reduces BP and improves CV health. Because exercise improves fitness and may also improve body composition and regional fat distribution, the associations of change in these parameters to BP change will be analyzed. Dual energy x-ray absorptiometry (DEXA) and MRI will assess total and regional body composition. A follow-up 6 months after treatment will address the practical issues of whether subjects will continue to exercise on their own, residual effects on BP, and if antihypertensive medications can be avoided. The results from this study will expand the scientific knowledge that defines exercise guidelines for older men and women at risk for CVD because of their BP levels.